Why is it important to estimate?
The problem comes when we learn that Barkley’s friends are “pizza loving gorillas.” Barkley has no prior experience eating pizza with these friends. He can’t estimate how much pizza is needed.
The ability to estimate also helps determine if answers to math problems are reasonable. Sometimes we round numbers to be able to add or subtract them more easily. When we do this, we can get a “rough idea” or an estimate of the correct answer.
Engineers and scientists (or anyone for that matter) can be caught in situations when they don’t have a calculator available, but need to make decisions very quickly. They can use their ability to estimate to get a close answer so they can continue their work. Later, they can go back and check their estimate with a calculator.
The more practice or experience we have with numbers and amounts helps us estimate more accurately. This is a skill that we need to practice.
Why is it important to estimate? Activities
National Council of Teachers of Mathematics Standards:
Numbers and Operations
- Understanding meanings of operations and how they relate to one another
- Compute fluently and make reasonable estimates
- Understand measurable attributes of objects
- Apply appropriate techniques, tools, and formulas to determine measurements
This activity helps students practice estimating the mass of several objects.
This is what we already know about estimation:
- Estimating helps you plan ahead and check your work to see if your answers make sense.
- The ability to estimate also helps determine if answers to math problems are reasonable. Sometimes we round numbers to be able to add or subtract them more easily.
- The more practice or experience we have with numbers and amounts helps us estimate more accurately.
Activity – Estimate the Mass
Per group: balances, gram stackers or other known amounts of mass, various objects with different mass, paper to create a chart
- Students should work in groups of four to six.
- Each group will need a balance, a set of standard mass amounts, and a set of objects to be measured. For example, a set of objects could include a tennis ball, a pencil, a dictionary, a pack of flashcards, etc.
- Discuss the term “mass” with your students. Mass is the amount of material found in an object. Mass is measured in grams using a balance. If this is the first time that students have measured mass, practice this skill with them before starting this activity.
- Explain that students will be asked to estimate the mass of the items BEFORE they actually measure the mass of the items.
- Practice estimating with the group by holding up an object that is NOT in the set of objects to be measured. Pass the object around and ask students to “guess” the mass of the object. As a comparison, tell them that a paperclip is about one gram. Record “guesses” so that they can be seen.
- Measure the object. Discuss the differences between the student “guesses” and the actual mass. Record the actual mass of the object on the board and suggest that students remember this amount to help them with the activity. Let students hold the object whenever they may need it as a point of reference.
- Display the chart and ask students to copy the chart on their own paper.
- Ask students to begin the activity by holding one item and estimating its mass. Ask students to record their estimates in the correct column.
- As soon as the estimate is recorded, instruct students to measure the mass of the object. Show students how to calculate the “oops” column by finding the difference between the estimate and actual measurement.
- Instruct students to estimate and measure each item, one at a time.
- Discuss how “estimating” is a skill that improves with practice. Students should find that their estimates are more accurate with more practice.
Discuss other situations when estimating is a helpful skill.